FIG. 17 is a block diagram of conventional inertial force sensor 801. Inertial force sensor 801 includes detecting element 802 having an inertial force applied thereto, detecting circuit 803 for detecting the amount of inertia corresponding to the inertial force, low pass filter (LPF) 804 connected to an output port of detecting circuit 803, and correction circuit 805 for correcting an output of LPF 804. Correction circuit 805 includes correction amount memory 806 for storing a correction amount written form an outside, and corrector 807 connected to an output port of LPF 804 and the output side of correction amount memory 806. Corrector 807 corrects an output of LPF 804 based on the correction amount stored in correction amount memory 806.
Inertial force sensor 801 outputs a predetermined reference signal, such as zero, when an inertial force is not input to inertial force sensor 801. When an inertial force is input, inertial force sensor 801 is required to output a signal corresponding to this inertial force. Therefore, deviations in output caused by manufacturing variations of detecting element 802 and output offset (initial offset) that typically arises from an electrical offset of detecting circuit 803 are measured, and their correction values are stored in correction amount memory 806 of inertial force sensor 801 before shipment.
In addition to output offsets that arise in the manufacturing process of inertial force sensors, an output offset value also changes from its initial value when an ambient temperature rapidly changes during the operation of the inertial force sensor. To correct the output offset even if a temperature change occurs, a look-up table is provided in the manufacturing process by storing correction amounts for correcting the output offset due to a temperature charge in a non-volatile memory. By referring to this look-up table, an appropriate output offset can be applied, corresponding to any change in ambient temperature.
To create and install this look-up table in the manufacturing process before shipment, in which ambient temperatures and corresponding offset correction values are written, manufacturing processes and manufacturing costs of inertial force sensor 801 increase.
Inertial force sensor 801 is applicable to a circuit for detecting camera shake of camcorder. In this case, inertial force sensor 801 detects angular velocity as the inertial force to detect the camera shake. Then, inertial force sensor 801 outputs a correction angle signal corresponding to this detection result. In the camcorder, camera shake at turning on power can be reduced by not applying correction using the correction angle signal before normal angular velocity signal is obtained by the inertial force sensor on turning on the power.
In inertial force sensor 801, the output offset may occur even if the inertial force is not input when a stress is applied to detecting element 802 or due to aging variation or environment change after a correction value is written in before shipment. A high pass filter can be inserted to remove this offset. However, due to delay time of the high pass filter, it takes time until a detection signal is stabilized at starting correction by the inertial force sensor at turning on power or resuming from the sleep mode.
Patent Literatures 1 to 5 disclose conventional inertial force sensors similar to inertial force sensor 801.